What Grosses You Out?

This is SCIENCE FRIDAY. I'm Ira Flatow. What grosses you out, the sight of maggots squirming on a rotten piece of meat? How about a cockroach running around your spice cabinet when you turn the lights on at night? How about eating strange organ meat like sweetbreads, pancreas. Maybe just a doorknob is enough to give you the chills, touched by so many hands, or a toilet seat touched by - well, you know, there must be so many germs, right.

Well, where does that sense of disgust come from? Why is something that is disgusting to one person a delicacy to another? And does it serve a purpose, keep us safe from disease, for example? Just a few of the things discussed in my next guest's book, "That's Disgusting: Unraveling the Mysteries of Repulsion." Rachel Herz is the author. She's also a research psychologist and teaches at Brown University in Providence. She joins us from Rhode Island Public Radio. Welcome back.

RACHEL HERZ: Hi, Ira, it's very nice to talk to you again.

FLATOW: I have to say I enjoy saying the name of your book more than I think a lot of other books we review, "That's Disgusting."

HERZ: Well, I like how you say it, too.

FLATOW: You use the word in your book pure yuckiness. What does that mean?

HERZ: Well, that's basically trying to get at the really visceral, raw dimension of disgust that's not very common and not very thought-through. It's that really creepy, yucky feeling of, for instance, stepping in dog poop accidentally or, you know, looking into a public toilet and noticing that it hasn't been flushed and used a lot of times, that kind of thing.

So it's very physical and basic.

FLATOW: We should warn people, we're going to get disgusting this hour.

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FLATOW: But one of the fascinating things you learn in your book is these are things that have to be learned or traits. Not everybody's disgusted the same way. You learn how to be disgusted by things.

HERZ: Yeah, I mean, I think it comes to a big surprise for most people that the idea that, you know, toilet's not flushed and things like that would not be inherently disgusting. But actually we first learn that poop is disgusting with potty training, and that lesson usually takes place around the age of three.

But before that, you know, newborns and young children will play with their feces and have no problem. Young kids as well, older than three, have no problems, you know, picking up something dead off the ground and bringing it to mommy to show them and things like this that we really have to become socialized to learn what the signals of disgust are.

FLATOW: And interestingly, you open your book talking about some of the strange foods that people eat around the world to make a point that different cultures are disgusted by different things.

HERZ: Absolutely, and so that's a great place to see learning kind of writ large when you look a culture, and you see these vast differences in, for instance, what fermented deliciousness is preferred in any given culture and how another culture can consider it absolutely repulsive.

I think a great example, in fact, is cheese just because it's so simple, and for us it seems, most of the time I think, to be anything from a comfort food to a real delicacy. And for instance, Asians consider it to be the equivalent of cow excrement.

So the idea that we adore something, and other cultures find it hideous, you know, we think, well, that's not logical. But there are things in Asia that they eat that we would find entirely repulsive.

But the interesting underlying thing here is that none of these foods are in fact dangerous. So it's not like we're ingesting poisons, and don't those Asians know better than to be eating 100-year-old eggs, and they're going to be falling over any second, or don't those Westerners know that that cheese riddled with blue stuff is poison.

So it's interesting that all these products are in fact safe, and the origins of disgust are really about protecting us from things that would be poison.

FLATOW: Do - so there's no natural disgust genes in us that when we taste something, we spit it out thinking that's poisonous?

HERZ: Well, that's actually not true. It is the case that bitter is inherently unpleasant, and we will spit that out instantly if we can, if something bitter gets in our mouth, and that's because bitter is typically a signal for high levels of alkaloids, which typically signal poison.

And so the bitter taste reaction is hard-wired and is ingrained from birth, and we will try to expel those kinds of tasting things, but beyond that, the disgust reaction, which goes well beyond the idea of spitting out bitter taste, is learned and culturally determined.

FLATOW: You were mentioning that when you give even young infants a little taste of something a little bitter that they make the disgusting face right from the beginning.

HERZ: Right, that was actually one of the things that first really turned me on the field of disgust. I thought it was completely fascinating that a basic taste, like bitter, instantly from birth, would elicit the expression in a newborn that you would make if I said could you please hold your neighbor's dirty dentures.

FLATOW: Disgusting.

HERZ: So I think that - yes. But it's pretty - it's very interesting in the origins, and also the part of the brain that controls taste is the same as the part of the brain that controls disgust. So the fundamental origins of disgust are rooted in our perception of taste and particularly the rejection of bitter taste which, as I said before, tend to indicate toxins.

But from then, it really morphs into something very complex, abstract and uniquely human.

FLATOW: Is it possible to unlearn something that you learn to be disgusting?

HERZ: Yes, I think definitely - I mean, at least you can modulate it down. So people who, for example, have to be exposed to disgusting things for periods of time develop tolerances to them and find them OK. So for example people who are emergency workers or work in hospitals and have to deal with blood and guts and body fluids all the time may initially begin their jobs feeling highly repulsed by these sorts of things.

But then they just become used to it, and so we can definitely become inured to the signals of disgust. It's also the case that our culture, again, what we're used to can make a big difference in terms of what we find disgusting. If, you know, there are no sewers around, and waste is everywhere, then for instance the smell would be, you know, the smell equivalent maybe to a fast-food restaurant here.

FLATOW: But is repulsive the same as disgusting? I'm thinking of a smell like a skunk smell that's sort of universally disgusting, right? Or, I mean...

HERZ: No, I mean, I'm actually someone who likes the smell of skunk.

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HERZ: And I'm not alone, as a matter of fact. I've met many people to confess to this. And interestingly, you know, smell is my primary area of expertise, and I discovered while working on disgust that there are a lot of fundamental commonalities.

And the reason why, for instance, the smell of skunk is not universally unpleasant is because our responses to smell are learned, just like our responses to disgust are. So if you first encounter the smell of skunk in a context where you thought it was a good smell, you will then think it's a good smell. And if you didn't get schooled in eww, that's disgusting, you'll be surprised later on if you make this confession.

FLATOW: I have heard other people say that. But I guess what I meant to say was that the skunk has that smell for a reason, right, and it must be because most things, or most animals, find it disgusting and repulsive.

HERZ: Well, it's dealing with its own specific local predators, and we are not part of the skunk, you know, typical predator domain. I mean, we don't go around eating them. We may accidentally kill them by running them over, but we are not part of the skunk natural predator system.

So the natural predators of skunk would be repelled by that scent. So we don't necessarily fall into that category, and that's why there's nothing built in for us.

HELENE: Well, I'm hoping that you can solve a lifelong problem for me. I was raised a vegetarian, as were my kids, and I cannot for the life of me figure out how people decide to be utterly repulsed by one kind of dead animal where they think that the other kind of dead animal looks good, smells good, tastes good. And, yeah, I'm just curious to hear the answer to that.

FLATOW: You mean like why someone who's a meat-eater can eat a cow but not a cat, or a cat is repulsive...?

HELENE: Exactly, you've got it, right there. Like when my kids, someone gave our family a ham one time for Christmas, and my kids carried it out and buried it, and they were just grossed out, while I realize it's somewhat, from what you're saying, societal. But there has to be more to it than that because people get really grossed out over a cat but not a cow, and they're both dead.

FLATOW: Well, some people eat cats, don't they?

HERZ: Well, that's actually a great question, and in fact there are cultures, for instance, in China where cats can be eaten. And your issue about pets versus the things we find in the supermarket is exactly the issue of an animal that we bring into our home and bring into our family.

So we bring our cats and dogs into our lives like we bring children in, and the idea of eating them is close to the concept of cannibalism and, you know, completely abhorrent whereas the things that we see in the supermarket when we go to the meat section, first of all it's lost all connection to its animal origins.

You know, you don't see the animal. You see this carved piece of something-or-other that's been bled, it's been packaged, it's in cellophane. So here's this thing, this protein that you enjoy consuming, and you purchase it. I've actually wondered, if people had to do more serious hunting, you know, whether or not they would be a little bit more reluctant to eat food and/or if we had to see, you know, eye-to-eye the whole cow, you know, hanging dead in the butcher shop whether we would be so excited about a filet mignon.

But again, I think it's our experience, and the key thing here is it's the meaning that we apply to the trigger that determines whether or not it's disgusting or acceptable or even delicious.

FLATOW: Gabriel(ph) in Palo Alto, hi, welcome to SCIENCE FRIDAY.

GABRIEL: Hi, Ira. Thank you. Great show.

FLATOW: Thank you.

GABRIEL: We're originally from Mexico. And the question is - papaya is actually a fairly frequent staple food, and I find the smell - it tastes - it just smells like vomit to me. And my wife and daughter absolutely love it. And I found that this is - that I'm not the only case. But I'm curious of how to - how do same foods can have such different impact on the smell? I'll take my answer off the air. Thank you.

FLATOW: OK.

HERZ: So that's also a very interesting question, and part of it may have been Gabriel's original experiences with the smell of papaya being different from his wife and his daughter. But it's also the case that recent genetic work has discovered that, in fact, everybody has a unique nose. And Gabriel may have certain receptors inside his nose that are particularly attuned to one or two aspects of the papaya bouquet that make it unpleasant for him, whereas his wife and his daughter do not. And potentially, the other people he knows have the same issue, or they have a combination of this issue, plus a bad experience with a papaya in the past.

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FLATOW: You write in your book getting off of foods for a little bit about other disgusts, that people are disgusted with their bodies. Why would our bodies disgust us?

HERZ: Well, we're not usually so disgusted by our bodies, but we're disgusted by other people's bodies, and specifically the things that come from their bodies. And that's because one of the key features of the emotion of disgust is to keep the outside - especially outside stuff coming from other people - away from our inside. And this is the connection with disease, as well. So we want to protect ourselves from becoming contaminated by the cooties and the oozy-gooeys of other people.

However, again, the situation and the context makes an enormous difference. So, you know, a stranger's saliva - someone who licks your face in a grocery store, for example, that you have no idea who they are - that's going to be horrendously repulsive. But if your lover does that to you in the bedroom, it could be totally erotic. So again, it's the meaning of the situation. It's the meaning of the trigger that determines if it's disgusting or delightful.

FLATOW: So that - odors that you give off may not smell so bad to yourself, but the same odors that someone else gives off smells awful.

HERZ: Absolutely and - yeah. Absolutely. And it's not just our own odors. We think that the odors of the things that are - make our family or ourselves are also OK. So, for example, if you're changing your own baby's diaper, that dirty nappy smells OK to you, but if you had another infant of the same age, their dirty diaper would smell gross. And even the case that we think that our own dog's breath is better than a stranger's dog's breath. So, you know, the things that we bring into our family, into our home, the intimates, those people are OK when it comes to their body products, typically. But the outsider, the stranger, that's where it gets dubious and disgusting.

FLATOW: Talking with Rachel Herz, author of "That's Disgusting: Unraveling the Mysteries of Repulsion," on SCIENCE FRIDAY from NPR. I'm Ira Flatow, being happy to be disgusting this afternoon with you. Let's go to the phones and see who else can join the crowd. Erin in Salt Lake City. Hi, Erin.

ERIN: Hi.

FLATOW: Hi, there.

ERIN: So this parlays nicely into what you guys were just talking about. I'm a nurse practitioner. And in the medical field, it's kind of a longstanding joke that there are certain things - you know, one person can deal with blood and guts, but another person can't. Or one person deals with the top part of the body, and the other person can't stand that part, but can deal with the bottom part of the body. And I just find that really fascinating that, you know, that - those things that disgust us sort of translate into this.

Well, my one thing, I can't handle oral care, or I can't handle blood or poop or pee. So I think it's really interesting that that's kind of, you know, translates into the medical profession, as well. And I'll take comments off the air.

ERIN: Certain things, for me, it's cough and sputum. No, it does not get any easier. But I'm a women's health nurse practitioner, and so lots of people would find what I do quite disgusting.

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FLATOW: Yeah. Well, thank you for sharing that with us, Erin.

ERIN: Yeah. (Unintelligible).

FLATOW: Have a good weekend. Bye. And she - do people get better acclimated, Rachel, as they get older to what's disgusting, or being more accommodating?

HERZ: People definitely get better acclimated as they get older. But just going back to Erin's point, it's also the case that we all have our disgust personality predisposition. So one person may be more disgusted by certain things - let's say oral care - and someone else is more disgusted by poop, or someone else is more disgusted by dead things and someone else is more disgusted by blood. So, you know - or moral issues. So it really depends. It's actually a personality variable, as well.

But it's also the case that everybody, regardless of their personality, as they get older, they get less disgust sensitive, and it's not necessarily clear why that happens, but there are some interesting hypotheses, if you'd like me to share them.

FLATOW: Sure, sure.

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HERZ: Well, one idea sort of stems back from everything we've been saying so far, which is just that as your - you get older, you've been there, done that, seen it so many times, smelled it so many times, et cetera, so you're more used to it. It's less disgusting. Another possibility is that the neurotransmitters in the brain that are controlling the disgust experience are damping down. They're less active. There's less of it. So we get less of an intense response. But what I think sort of philosophically is my favorite possibility is that disgust really, at its core, is about our fear of death and our trying to protect ourselves from death in all sorts of ways.

And as we get to the end of our life, maybe we've become somewhat more accepting of that fact, and therefore, the whole gamut of things that are disgusting become less of an issue or a problem for us.

FLATOW: Does disgust about morality work the same way - violence, disgusted with violence and, you know, things like that?

HERZ: Well, again, I think it's - you know, that's certainly a great question, and it has to do both with your exposure and your experience. For instance, you know, if you're exposed to a lot of violence and a lot of bloodshed, I think that you do definitely become inure to it. At the same time, I think certain professions - like if you're a police officer, for instance, and you have to deal with shootouts and accidents and that sort of stuff, because you're constantly reminded of your mortality - in fact, you know, assuming that you're not particularly old, you might become more disgusted of things.

Because, in fact, when we're reminded of our eminent demise or, you know, demise at some point, we do become more disgust-sensitive. So it could work in a variety of ways.

FLATOW: All right. We're going to take a short break and come back more and talk with Rachel Herz. She's author of "That's Disgusting: Unraveling the Mysteries of Repulsion." Our number: 1-800-989-8255. You can also tweet us @scifri, @-S-C-I-F-R-I. We want to hear about what disgusts you, but only if we can say it on the radio. So stay with us. We'll be right back after this break.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.

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FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're talking with Rachel Herz about her book "That's Disgusting" - not her, the book title - "Unraveling the Mysteries of Repulsion." Our number" 1-800-989-8255. One last question for you. That - I was thinking, reading the book is, why are we drawn to horror movies, you know, which feature dismembered bodies, gory stuff, chainsaw massacres, things like that?

HERZ: Well, that's also a fantastic question, and it's connected to the issue of death again, and something else. So, first of all, with respect to death, I think that the horror show enables us to explore some of the mystery of the extremes of death - you know, Freddie killing all these people in incredibly crazy ways - and we think, well, you know, it couldn't be that bad. So if we can tolerate that, then maybe some of the fear of our real death is attenuated somewhat, and sort of the mystery is taken out a little bit.

Another answer to the question is to do with this seemingly strange predilection that we have called benign masochism, and that is that we actually like to do things which seem dangerous or seem disgusting or horrifying, as long as they don't actually really hurt us. So, for example, bungee jumping, taking roller coaster rides, eating habanero peppers, doing those sort of things and going to see horror movies is like testing the limits, and we seem to enjoy doing that as long as it's not actually going to cause us harm.

FLATOW: Yeah. We used to call those cheap thrills back in the day.

HERZ: Yeah.

FLATOW: Yeah.

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FLATOW: Thank you very much, Rachel, for taking time to be with us today. A very enjoyable, very readable book, very exciting.